Flash bulb



July 2 ,1943. A. I. STEVENS arm. 2 ,9

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INVENTORS AITORNEYS Paten tecl July 20, 1943 FLASH BULB Arthur L.Stevens and Herman J. DInnocenzo, Buffalo, N. Y., assignors to Pierceand Stevens, Incorporated, Buffalo. N. Y.

Application January 23, 1941, Serial No. 375,642

3 Claims. (01. 67-31) This invention relates to an improved type offlash bulbfor photographic purposes or the like, and to improved methodsand means for coating the interiors thereof.

It is now known that flash bulbs may be greatly improved by coatingtheinteriors thereof with heat insulating and. structurally reinforcingcoating substance, whereby the bulbs may be of reduced wall thicknessand less liable to failure under operating conditions. For this purposecertain types of lacquersor like substances have'previously been appliedto the bulb interiors, but the uses of previous coating substances forthis purpose have been subject to certain serious disadvantages andobjections.

For example, certain cellulose derivatives, es-

pecially of the nitro cellulose type, have been employed previously forthis purpose, but such materials. have invariably been objection'ableeither from the standpoint of relatively high cost, lack, of sufficienttoughness or other strength or adhesion capabilities; tendency to charduring the bulb-sealing process or during the flash, thereby impairingthe light transmitting capacity of the finished product; inefliciency asa heat insulating medium for protection of the bulb glass; or the like.Consequently, it.has been attempted to improve the qualities of thecellulose derivative compositions of the prior art by compounding themwith plasticizers and resins or the like but this invariably makes theproduct more subject to charring under elevated temperature conditions,and thus the attainment of one objective is accompanied by introductionof another objectionable characterlstic. In addition, such modifiedcompositions are relatively expensive.

The primary object of the present invention is to provide an improvedform of flash bulb comprising a glass-wall bulb interiorly coated in animproved manner with a substance novel in this art whereby improvedflash performance is provided. Another object of the invention is toprovide an improved flash bulb comprising structurally an outer glassshell interiorly lined With a structurally reinforcing substance whichis relatively inexpensive and stable under the operating temperatures tobe met with, and of high light transmitting efficiency, and otherwiseunobjectionable from the standpoint of the manufacturer and the user.Other objects and advantages of the invention will appear in thespecification hereinafter.

The figure of the drawing is an elevational view of a conventional flashbulb treated according to the principles of the present invention.

In the drawing the numeral l0 designates the conventional glass envelophaving associated therewith a suitable connecting plug II ofconventional form. An igniting filament is indicated at l2 and thenumeral I3 designates the metal foil, usually aluminum or magnesium,which is employed for the propagation of actinic light by combustion ofthe metal. The numeral I4 designates an interior surface coating of anature to be described below and applied in pursuance to the method ofthe present invention.

To practice the invention it is preferred to employ a relativelythin-walled form of glass bulb shell fabricated of any presently knownsuitable form of glass material such as has previously been used inconnection with the manufacture of flash bulbs or the like. Beforeinsertion of the lighting filament and sealing of the bulb, the interiorof the shell is sprayed with a liquid composition comp-rising isobutylmethachrylate in a suitable solvent such as combination of toluo] andnaphtha. More specifically, the naphtha ingredient of the compositionabove referred to may be of the grade commercially designated aspetroleum naphtha having a boiling range of 55-100? C. and a specificgravity between .695 and .700 at 20 0.; and the relative proportions ofthe ingredients of the composition may be specifically; polynierizedisobutyl methachrylate-18%; toluol62%; naphtha-20%.

In the case of the'specific formula set forth just above the solventmixture has a boiling point of around degrees 0., thereby providingrelatively rapid drying of the coating composition when applied to theglass bulb. It will be understood that the specific formula givenhereinabove may be varied somewhat to provide satisfactory results, andit has been found, for example that the isobutyl methachrylateingredient of the coating composition may constitute between 15% and 25%of the ingredients, with satisfactory results. It has also beendetermined by experiment that. the toluol ingredient may be replaced byxylol, and that satisfactory results may also be obtained if the'naphthais replaced by benzol. Also, other ketones and esters may be employed ifdesired within the concept. of this invention.

7 The composition of the invention provides, in its initial liquidstate, a smooth flowing material which is adaptedto be sprayed againstthe interior of the bulb shell to provide a smooth and uniformly thickcoating thereon which immediately sets and thus avoids draining or theproduction of drawing irregularities such as would result in non-uniformthickness of the final coating. It has been found that the coating soprovided is of improved heat insulating capacity, and is inherentlytenacious with respect to the bulb shell. Consequently, an efficientheat insulating and structural reinforcing coating may be providedthrough use of a thicker application of coating material; and thus, inaddition to using a relatively inexpensive mixture for the purpose, lesscoating material is required and further economy is effected. Thecoating material of the invention is water-white and thereby transmitsall possible light rays. It is stable in the presence of temperaturesequal to those experienced during the flashing operation and does notchar during the flashing process. The material may be baked attemperatures as high as 375 C. without discoloration or otherdeleterious effect, and therefore does not become charred duringsubsequent sealing of the bulb. The decomposition. and reaction productsof the coating substance are non-discolored, and therefore maximum lightoutput of the flash bulb is permitted, even during high peakperformance. The superior adhesive properties of the coating compositionprovides, in combination with the glass of the bulb shell asubstantially integral structure, and the setting-up characteristics ofthe coating composition are such that the setting process is accompaniedby introduction of minimum stresses in the glass bulb shell.

Because the finished coating portion of the integral glass and coatingstructure is of thermoplastic nature the heating of the interior coatingportion of the structure does not permit stresses to be transferred fromthe coating element to the glass shell portion. The coating element ofthe finished bulb structure is substantially stable to light and aging,and does not turn yellow under either direct light or ultra-violet rays.It is an is of improved characteristics fromthe stand-' point of theuser and is relatively simple and inexpensive to manufacture. Theflash'bulbs of the invention are clearly distinguishable from flashbulbs of the prior art such as are interiorlycoated with nitro cellulosederivativ compositions which are subject to deterioration under aging orheat applying processes. For example, such coatings of the prior art aresubject to decomposition at about C., and are thereby difflcult toemploy with satisfactory results in view of the temperaturm required tosubsequently seal the bulbs. The coating composition of the invention isalso superior, for example, to polymers of the vinyl type which spiderweb when it is attempted .to spray them; whereas the coating compositionof the invention is adapted to be either sprayed or flushed on the glassshell surfaces to provide the. uniformly coated composite structurehereinabove described. 7

We claim:

1. A flash bulb having a casing comprising a I composite integralstructure having an outer glass shell and a continuous adherent innershell comprising isobutyl methacrylate, combustible material in saidcasing, and combustion supporting material likewise in said casing.

2. A flash bulb having a casing comprising a composite integralstructure having an outer glass shell coated interiorly with acontinuous adherent, interiorly-exposed layer of isobutyl methachrylateresin, and combustible material and combustion supporting material insaid casing.

3. A flash bulb having a casing comprising a composite integralstructure having an outer glass shell and an interior continuousadherent coating of a methachrylate resin, and combustible material andcombustion supporting material in said casing.

ARTHUR L. STEVENS. H. J DINNOCENZO.

